Erasable block segmentation for memory

ABSTRACT

Various embodiments comprise apparatuses such as those having a block of memory divided into sub-blocks that share a common data line. Each of the sub-blocks of the block of memory corresponds to a respective one of a number of segmented sources. Each of the segmented sources is electrically isolated from the other segmented sources of the block of memory. Additional apparatuses and methods of operation are described.

BACKGROUND

Computers and other electronic systems, for example, digitaltelevisions, digital cameras, and cellular phones, often have one ormore memory devices to store information. Increasingly, memory devicesare being reduced in size to achieve a higher density of storagecapacity. Even when increased density is achieved, consumers oftendemand that memory devices also use less power while maintaining highspeed access.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a memory device having a memory array withmemory cells, according to an embodiment;

FIG. 2 is a simplified schematic diagram of a portion of a memory blockhaving segmented sources, according to various embodiments;

FIG. 3 is a plan view of the portion of the memory block of FIG. 2,showing an example of erasable sub-blocks of the memory;

FIG. 4 is a graph of bias conditions that may exist within the memoryblock of FIG. 3; and

FIG. 5 is a block diagram of a system embodiment, including a memorydevice.

DETAILED DESCRIPTION

The description that follows includes illustrative apparatuses(circuitry, devices, structures, systems, and the like) and methods(e.g., processes, sequences, techniques, and technologies) that embodythe subject matter. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providean understanding of various embodiments of the subject matter. Afterreading this disclosure, it will be evident to those of ordinary skillin the art however, that various embodiments of the subject matter maybe practiced without these specific details. Further, well-knownapparatuses and methods have not been shown in detail so as not toobscure the description of various embodiments.

To increase the density of a memory device, memory designers considerthe area (e.g., footprint) on an underlying substrate for a memory cell.A memory cell may be defined by a feature size, F, where F is theminimum feature size due to various processing limitations, such aslithography limitations, including the numerical aperture and wavelengthof the photolithographic systems employed. The memory cell area may havedimensions of 2 F by 2 F, or 4 F². In some two-dimensional NAND memorystructures, only one memory cell resides in a 4 F² area. In athree-dimensional (3D) NAND memory structure, there may be N tiers(e.g., layers) of memory cells where the memory cells are stacked, oneabove another, to form the N tiers. Therefore, in these structures, eachmemory cell may still be defined by the 4 F² area. However, there are Nmemory cells within that area due to the 3D structure.

To further illustrate, a NAND string of memory cells is formed between asource (e.g., a source line, source slot, or source diffusion region)and a data line as is known independently in the art. A block of memoryis comprised of a number of pages. The block is the smallest chunk ofmemory that a user can erase at one time. Contemporaneous devices mayhave, for example, 32 kilobytes erasable by a common source and a singledata line. In a two-dimensional (e.g., planar) memory array, a singleblock may have two to four megabytes of memory. A 3D memory array mayoccupy the same area on the substrate but have a much higher density.For example, the block size can be between eight and 16 megabytes, orhigher, for the same sized area on the substrate of a two-dimensionalmemory array. Thus, the 3D memory density can be four times the memoryof the two-dimensional array. Consequently, the block size in a 3Dmemory array is usually larger than the 2D memory array.

One detrimental side effect of this increase in memory density for thesame area on the substrate is that the number of simultaneously erasablepages of memory in a block is also increased. For example, if the numberof tiers in the 3D NAND memory array is doubled, the number of pages perblock can quadruple. In many applications, the increase in block size isinconvenient or even intolerable. Thus, the various embodimentsdescribed herein reduce the erasable block size.

In various embodiments described herein, smaller erasable blocks can beachieved by segmenting the global sources and drain select lines withineach physical block. Segmentation of the global source allows an eraseoperation to be limited to one or more selected sub-blocks. Thesegmented drain select lines are formed to correspond with segmentedsource lines within each sub-block.

Further, junctions at either end of the NAND string connected to selectgate, source-side (SGS) or select gate drain-side (SGD) devices can bedesigned to have different breakdown voltage depending on which junctionis used to initiate the needed erase voltage in the NAND string. Forexample, if the SGS device is used to initiate the erase voltage thenone can design its breakdown voltage to be lower than the SGD devicejunction. The higher SGD breakdown voltage should help prevent an erasedisturb of memory cells in adjacent non-selected sub-blocks bypreventing the developed erase voltage to be transmitted to adjacent subblocks. Examples of erase bias conditions are also described herein toimplement the erase operation within individual sub-blocks.

Referring now to FIG. 1, a block diagram of an apparatus in the form ofa memory device 101 is shown. The memory device 101 includes one or morememory arrays 102 having a number (e.g., one or more) of memory cells100 according to an embodiment. The memory cells 100 can be arranged inrows and columns along with access lines 104 (e.g., wordlines to conductsignals WL0 through WLm) and first data lines 106 (e.g., bit lines toconduct signals BL0 through BLn). The memory device 101 can use theaccess lines 104 and the first data lines 106 to transfer information toand from the memory cells 100. A row decoder 107 and a column decoder108 decode address signals A0 through AX on address lines 109 todetermine which ones of the memory cells 100 are to be accessed.

Sense circuitry, such as a sense amplifier circuit 110, operates todetermine the values of information read from the memory cells 100 inthe form of signals on the first data lines 106. The sense amplifiercircuit 110 can also use the signals on the first data lines 106 todetermine the values of information to be written to the memory cells100.

The memory device 101 is further shown to include circuitry 112 totransfer values of information between the memory array 102 andinput/output (I/O) lines 105. Signals DQ0 through DQN on the I/O lines105 can represent values of information read from or to be written intothe memory cells 100. The I/O lines 105 can include nodes of the memorydevice 101 (e.g., pins, solder balls, or other interconnect technologiessuch as controlled collapse chip connection (C4), or flip chip attach(FCA)) on a package where the memory device 101 resides. Other devicesexternal to the memory device 101 (e.g., a memory controller or aprocessor, not shown in FIG. 1) can communicate with the memory device101 through the I/O lines 105, the address lines 109, or the controllines 120.

The memory device 101 can perform memory operations, such as a readoperation, to read values of information from selected ones of thememory cells 100 and a programming operation (also referred to as awrite operation) to program (e.g., to write) information into selectedones of the memory cells 100. The memory device 101 can also perform amemory erase operation to clear information from some or all of thememory cells 100.

A memory control unit 118 controls memory operations using signals onthe control lines 120. Examples of the signals on the control lines 120can include one or more clock signals and other signals to indicatewhich operation (e.g., a programming operation or read operation) thememory device 101 can or should perform. Other devices external to thememory device 101 (e.g., a processor or a memory controller) can controlthe values of the control signals on the control lines 120. Specificcombinations of values of the signals on the control lines 120 canproduce a command (e.g., a programming, read, or erase command) that cancause the memory device 101 to perform a corresponding memory operation(e.g., a program, read, or erase operation).

Although various embodiments discussed herein use examples relating to asingle-bit memory storage concept for ease in understanding, theinventive subject matter can be applied to numerous multiple-bit schemesas well. For example, each of the memory cells 100 can be programmed toa different one of at least two data states to represent, for example, avalue of a fractional bit, the value of a single bit or the value ofmultiple bits such as two, three, four, or a higher number of bits.

For example, each of the memory cells 100 can be programmed to one oftwo data states to represent a binary value of “0” or “1” in a singlebit. Such a cell is sometimes called a single-level cell (SLC).

In another example, each of the memory cells 100 can be programmed toone of more than two data states to represent a value of, for example,multiple bits, such as one of four possible values “00,” “01,” “10,” and“11” for two bits, one of eight possible values “000,” “001,” “010,”“011,” “100,” “101,” “110,” and “111” for three bits, or one of anotherset of values for larger numbers of multiple bits. A cell that can beprogrammed to one of more than two data states is sometimes referred toas a multi-level cell (MLC). Various operations on these types of cellsare discussed in more detail, below.

The memory device 101 can receive a supply voltage, including supplyvoltage signals V_(cc) and V_(ss), on a first supply line 130 and asecond supply line 132, respectively. Supply voltage signal V_(ss) can,for example, be at a ground potential (e.g., having a value ofapproximately zero volts). Supply voltage signal V_(cc) can include anexternal voltage supplied to the memory device 101 from an externalpower source such as a battery or alternating-current to direct-current(AC-DC) converter circuitry (not shown in FIG. 1).

The circuitry 112 of the memory device 101 is further shown to include aselect circuit 115 and an input/output (I/O) circuit 116. The selectcircuit 115 can respond to signals SEL1 through SELn to select signalson the first data lines 106 and the second data lines 113 that canrepresent the values of information to be read from or to be programmedinto the memory cells 100. The column decoder 108 can selectivelyactivate the SEL1 through SELn signals based on the A0 through AXaddress signals present on the address lines 109. The select circuit 115can select the signals on the first data lines 106 and the second datalines 113 to provide communication between the memory array 102 and theI/O circuit 116 during read and programming operations.

The memory device 101 may comprise a non-volatile memory device, and thememory cells 100 can include non-volatile memory cells, such that thememory cells 100 can retain information stored therein when power (e.g.,V_(cc), or V_(ss), or both) is disconnected from the memory device 101.

Each of the memory cells 100 can include a memory element havingmaterial, at least a portion of which can be programmed to a desireddata state (e.g., by being programmed to a corresponding charge storagestate). Different data states can thus represent different values ofinformation programmed into each of the memory cells 100.

The memory device 101 can perform a programming operation when itreceives (e.g., from an external processor or a memory controller) aprogramming command and a value of information to be programmed into oneor more selected ones of the memory cells 100. Based on the value of theinformation, the memory device 101 can program the selected memory cellsto appropriate data states to represent the values of the information tobe stored therein.

One of ordinary skill in the art may recognize that the memory device101 may include other components, at least some of which are discussedherein. However, several of these components are not shown in thefigure, so as not to obscure details of the various embodimentsdescribed. The memory device 101 may include devices and memory cells,and operate using memory operations (e.g., programming and eraseoperations) similar to or identical to those described below withreference to various other figures and embodiments discussed herein.

With concurrent reference now to FIG. 2 and FIG. 3, a simplifiedschematic diagram of a portion of a memory block 200 having sub-blocks,according to various embodiments, is shown. FIG. 3 shows a plan view 300of the schematic diagram of FIG. 2.

For ease in understanding the subject matter, only one portion of athree-dimensional memory structure is shown. As will be apparent to aperson of ordinary skill in the art, the portion of the memory block 200may be one portion of a block formed substantially normal to a face ofan underlying substrate on which the memory is formed. For example, NANDmemory cell strings are arranged substantially perpendicular relative toa face of the substrate. Conventional 3D memory structures are knownindependently in the art.

The portion of the memory block 200 includes a left-side sub-block 210and a right-side sub-block 230. However, the disclosed subject matter isnot limited to left and right sub-blocks. Sub-blocks may be arranged invarious configurations and include varying numbers of strings of memorycells. The number of sub-blocks may be in the hundreds or more,depending on the size of the memory block and the number of strings persub-block. Additionally, the various embodiments described herein may beused with various types of electronic devices.

Each of the left-side sub-block 210 and the right-side sub-block 230include a number of NAND memory cell strings 201A, 201B, . . . , 201 n.A common bit line 219 is coupled to each of the strings. Although theillustrated portion of the memory block 200 shows only one bit line andsix memory cell strings for ease of illustration and discussion, a blocktypically includes many more bit lines and memory cell strings. The NANDmemory cell strings 201A, 201B, 201C in the left-side sub-block 210 eachinclude a number of memory cells 205L. Similarly, each of the NANDmemory cell strings 201 n-2, 201 n-1, 201 n in the right-side sub-block230 includes a number of memory cells 205R. Each of the sub-blockstherefore comprises a number of non-overlapping ones of the memory cellstrings 201. For example, the non-overlapping strings indicate that eachmemory cell/string is only contained within one sub-block. Therefore, nosub-blocks share a memory cell/string.

Each end of the NAND memory cell strings 201A, 201B, 201C in theleft-side sub-block 210 is coupled to one of a left-side drain selectdevice 203A, 203B, 203C and a left-side source select device 207A, 207B,207C. Each end of the NAND memory cell strings 201 n-2, 201 n-1, 201 nin the right-side sub-block 230 is coupled to one of a right-side drainselect device 203 n-2, 203 n-1, 203 n and a right-side source selectdevice 207 n-2, 207 n-1, 207 n. Each gate on the source select devices207A . . . 207 n is coupled to a common source select (SGS) line 221.

The left-side sub-block 210 and the right-side sub-block 230 eachinclude a separate set of drain select devices. The left-side sub-block210 has left-side drain select devices 203A, 203B, 203C. The right-sidesub-block 230 has right-side drain select devices 203 n-2, 203 n-1, 203n. Gates of the left-side drain select devices 203A, 203B, 203C are eachcoupled separately to left-side select gate on drain side (SGD) lines211 that can receive signals SGD0, SGD1, SGD2, respectively, while gatesof the right-side drain select devices 203 n-2, 203 n-1, 203 n are eachcoupled separately to right-side SGD lines 215, that can receive signalsSGD0′, SGD1′, SGD2′, respectively. Separate bias level may be applied toeach of the left-side SGD lines 211 and the right-side SGD lines 215.

Further, each of the left-side sub-block 210 and the right-sidesub-block 230 has a separate segmented source; a left-side source 213and a right-side source 217. The left-side source 213 and a right-sidesource 217 can therefore be biased with separate bias signals, SL0 andSL1, respectively. Consequently, a separate bias level may be applied toeach of the left-side source 213 and a right-side source 217. Examplesof various bias signals as they might exist within the memory block 200are described below with reference to FIG. 4.

Thus, the SGD lines and the source are segmented within the block, witheach of the segmented sources 213, 217 of the block corresponding to arespective one of a number of sub-blocks. For example, each portion ofthe memory block 200 comprising a sub-block has physically segmentedsources and drain select lines. Since the sources and drain select linesare physically segmented, the segmented source in one sub-block iselectrically isolated from the segmented sources in other sub-blocks. Invarious embodiments, bit lines, word lines, and source select lines areshared in common between sub-blocks. In other embodiments, the bitlines, word lines, and source select lines may be segmented betweensub-blocks.

The portion of the memory block 200 also shows a number of word lines250. Although the figure indicates there are a total of 32 word lines,the exact number of word lines is irrelevant to the disclosed subjectmatter. Any higher number or lower number of word lines may be used withthe various embodiments described herein. As is evident to a person ofordinary skill in the art, lines labeled WL and the bit line 219 in FIG.2 may correspond to any one of the access lines 104 and any one of thefirst data lines 106 of FIG. 1, respectively.

Referring now to FIG. 3, the plan view 300 of the memory block 200 ofFIG. 2 indicates a number of data lines 310 (e.g., bit lines) coupled atpoints 301 to pillars within each NAND memory cell strings 201A, 201B, .. . , 201 n. The points 301 may also be considered a connection pointfrom the NAND memory cell strings to selected ones of the data lines310. Although the figure indicates 16 data lines (e.g., bit lines), theexact number of word lines is irrelevant to the disclosed subjectmatter. Any higher or lower numbers of data lines may be used with thevarious embodiments described herein.

The arrangements shown, by way of example, in FIG. 2 and FIG. 3, allowcreating erasable sub-blocks without the need to segment the data lines310 and create independent banks of data lines and associated circuitry(e.g., independent sense circuitry). The creation of independent banksof data lines and associated circuitry would otherwise result in asignificant increase in cost and a commensurate increase in area (e.g.,footprint) of the memory device. As discussed herein, a lower SGDjunction breakdown relative to the SGS junction breakdown can prevent anerase voltage initiated by one source to propagate to the othersub-block via the data lines.

FIG. 4 is a graph 400 of bias conditions that may exist within thememory block of FIG. 2. In FIG. 4, an example of signals that can beapplied to erase the memory cells 205R in the right-side sub-block 230while attempting to prevent an erase or erase disturb to the memorycells 205L in the left-side sub-block 210 is shown. When the mechanismsdescribed herein are not used, an erase signal applied within one of thesub-blocks selected for an erase operation may cause an erase disturb,or possibly a complete erasing, of the memory cells in the othernon-selected sub-block.

As described previously, the portion of the memory block 200 hasphysically segmented sources 213, 217 and drain select lines for thesub-blocks 210, 230. The SL1 signal on the right-side source 217 causescurrent to flow through the channel of each of the memory cells 205R inthe NAND memory cell strings 201 in the right-side sub-block 230,raising the channel potential of strings attached to SL1 in FIG. 2.However, a reverse junction bias condition in the left-side drain selectdevices 203A, 203B, 203C may allow current to flow from the bit line 219to the memory cells 205L in the left-side sub-block 210. Consequently,the memory cells 205L in the non-selected left-side sub-block 210 shouldbe protected to prevent an unintentional erase or erase disturb.

With reference again to FIG. 4, the graph 400 indicates that the SGDlines coupled to the SGD devices 203 of the selected right-sidesub-block 230, and SGS line 221, are allowed to float. A bias level 407(SL1) applied to segmented source 217 of the selected right-sidesub-block 230, is raised to 20 V while a bias level 405 (SL0) of 10 V isapplied to segmented source 213. The bias level 407 at 20 V issufficient to allow erasure of the memory cells 205L in the right-sidesub-block 230. However, the bias level 407 (SL0) at 10 V prevents (or atleast substantially reduces) the unintentional erasure of the memorycells 205R. The bias level 407 (SL0) at 10 V may prevent the SGDjunctions connected to the common data lines from reaching sufficientbreakdown voltage levels to cause a leak back from the data line tochannels of the memory cells 205L. This can be achieved by initiallysetting the channel potential in devices on the left side to someintermediate levels (e.g., a level not high enough to cause an erasedisturb). Initializing SL0 to a voltage around 10 V (e.g., between about0 V to about 10 V, in general) initializes the channel in the left sideto a higher intermediate potential thereby reducing the SGD junctionpotential on the data line side when SL1 is raised to 20V.

Keeping the bias level 403 on the drain select lines 211 coupled to theSGD device 203A, for example, at an SGD0 value no more than 15 V (orapproximately 75% of the bias level 407 applied to segmented source217), prevents gate oxide breakdown to occur in left side SGD devicesand help the reverse bias condition discussed above not to occur. Thisprevents the voltage on the bit line 219 causing an erase disturb in thememory cells 205L. Ensuring that the SGD junction breakdown voltage isless than the SGS junction breakdown, only approximately 10 V (in thisexample) is another important design feature preventing BL voltagetransfer to 205L devices preventing erase disturb. As described above,10 V is insufficient to effect an erase disturb condition. Consequently,a selection of applied bias voltage, a segmented source, and/or designof the breakdown voltage for the SGD devices allow sub-blocks within amemory device to be selectively erased while preventing (or at leastsubstantially reducing) an erase disturb of memory cells in non-selectedsub-blocks. In this way, selected sub-blocks can be erased at will.

Optimization of breakdown voltages within a device is knownindependently in the art and may include dopant selection and dopantprofiling within the device. Additionally, junctions within the variousdevices may be formed so that the breakdown voltages are on the variousdevices may be asymmetric (e.g., the SGD junction on the data line sideversus the SGS junction on the source side).

Based on reading and understanding the disclosure provided herein, aperson of ordinary skill in the art may readily extend the techniquesand concepts to any number and various arrangements of memory cells. Forexample, the person of ordinary skill in the art can apply thetechniques and concepts to a memory block with hundreds, thousands, oreven more sub-blocks. Thus, many embodiments may be realized.

For example, a system 500 of FIG. 5 is shown to include a controller503, an input/output (I/O) device 511 (e.g., a keypad, a touchscreen, ora display), a memory device 509, a wireless interface 507, a staticrandom access memory (SRAM) device 501, and a shift register 515,coupled to each other via a bus 513. A battery 505 may supply power tothe system 500 in one embodiment. The memory device 509 may include aNAND memory, a flash memory, a NOR memory, a combination of these, orthe like.

The controller 503 may include, for example, one or moremicroprocessors, digital signal processors, micro-controllers, or thelike. The memory device 509 may be used to store information transmittedto or by the system 500. The memory device 509 may optionally also beused to store information in the form of instructions that are executedby the controller 503 during operation of the system 500 and may be usedto store information in the form of user data either generated,collected, or received by the system 500 (such as image data). Theinstructions may be stored as digital information and the user data, asdisclosed herein, may be stored in one section of the memory as digitalinformation and in another section as analog information. As anotherexample, a given section at one time may be labeled to store digitalinformation and then later may be reallocated and reconfigured to storeanalog information. The controller 503, the memory device 509, andand/or the shift register 515 may include one or more of the novelmemory devices described herein.

The I/O device 511 may be used to generate information. The system 500may use the wireless interface 507 to transmit and receive informationto and from a wireless communication network with a radio frequency (RF)signal. Examples of the wireless interface 507 may include an antenna,or a wireless transceiver, such as a dipole antenna. However, the scopeof the inventive subject matter is not limited in this respect. Also,the I/O device 511 may deliver a signal reflecting what is stored aseither a digital output (if digital information was stored), or as ananalog output (if analog information was stored). While an example in awireless application is provided above, embodiments of the inventivesubject matter disclosed herein may also be used in non-wirelessapplications as well. The I/O device 511 may include one or more of thenovel memory devices described herein.

The various illustrations of the methods and apparatuses are intended toprovide a general understanding of the structure of various embodimentsand are not intended to provide a complete description of all theelements and features of the apparatuses and methods that might make useof the structures, features, and techniques described herein.

The apparatuses of the various embodiments may include or be includedin, for example, electronic circuitry used in high-speed computers,communication and signal processing circuitry, single or multi-processormodules, single or multiple embedded processors, multi-core processors,data switches, and application-specific modules including multilayer,multi-chip modules, or the like. Such apparatuses may further beincluded as sub-components within a variety of electronic systems, suchas televisions, cellular telephones, personal computers (e.g., laptopcomputers, desktop computers, handheld computers, tablet computers,etc.), workstations, radios, video players, audio players, vehicles,medical devices (e.g., heart monitors, blood pressure monitors, etc.),set top boxes, and various other electronic systems.

A person of ordinary skill in the art will appreciate that, for this andother methods (e.g., erase operations) disclosed herein, the activitiesforming part of various methods may be implemented in a differing order,as well as repeated, executed simultaneously, with various elements orbias levels substituted one for another. Further, the outlined acts andoperations are only provided as examples, and some of the acts andoperations may be optional, combined into fewer acts and operations, orexpanded into additional acts and operations without detracting from theessence of the disclosed embodiments.

The present disclosure is therefore not to be limited in terms of theparticular embodiments described in this application, which are intendedas illustrations of various aspects. Many modifications and variationscan be made, as will be apparent to a person of ordinary skill in theart upon reading and understanding the disclosure. Functionallyequivalent methods and apparatuses within the scope of the disclosure,in addition to those enumerated herein, will be apparent to a person ofordinary skill in the art from the foregoing descriptions. Portions andfeatures of some embodiments may be included in, or substituted for,those of others. Many other embodiments will be apparent to those ofordinary skill in the art upon reading and understanding the descriptionprovided herein. Such modifications and variations are intended to fallwithin a scope of the appended claims. The present disclosure is to belimited only by the terms of the appended claims, along with the fullscope of equivalents to which such claims are entitled. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting.

In various embodiments, an apparatus is provided that includes a blockof memory having sub-blocks that share a common data line. Each of thesub-blocks of the block of memory corresponds to a respective one of anumber of segmented sources. Each of the segmented sources of the blockof memory is electrically isolated from the other segmented sources ofthe block of memory.

In at least some of the embodiments of the apparatus, the sub-blocks ofthe block of memory share a number of common access lines. Each of thecommon access lines corresponds to a respective one of a number of tiersof memory cells in the block of memory.

In at least some of the embodiments of the apparatus, each of thesub-blocks of the block of memory comprises a respective number ofstrings of memory cells. Each of the strings of memory cells are coupledto the common data line through a respective drain select device and tothe respective segmented source through a respective source selectdevice. The source select devices have a higher breakdown voltage thanthe drain select devices.

In various embodiments, a three-dimensional device is provided thatincludes multiple tiers of memory cells. The three-dimensional deviceincludes a first sub-block of a block of memory having a first number ofmemory cell strings and a first segmented source, and a second sub-blockof the block of memory having a second number of memory cell strings anda second segmented source. The first and second segmented sources areelectrically isolated.

In at least some of the embodiments of the three-dimensional device,each of the first number of memory cell strings is coupled to arespective one of a first number of drain select devices and each of thesecond number of memory cell strings is coupled to a respective one of asecond number of drain select devices.

In at least some of the embodiments of the three-dimensional device,each of the first number of memory cell strings is coupled to a commondata line through a respective one of the first number of drain selectdevices and each of the second number of memory cell strings is coupledto the common data line through a respective one of the second number ofdrain select devices.

In various embodiments, an apparatus is provided that includes a blockof memory having a first sub-block and a second sub-block. The firstsub-block and the second sub-block include a first number of memory cellstrings and a second number of memory cell strings, respectively. Theblock of memory further includes a first segmented source coupled to thefirst number of memory cell strings in the first sub-block through afirst number of source select devices, and a second segmented sourcecoupled to the second number of memory cell strings in the secondsub-block through a second number of source select devices. The sourceselect devices having a higher breakdown voltage than the drain selectdevices.

In various embodiments, an electronic device is provided that includes ablock of memory having a number of memory cell strings. Each of thememory cell strings including respective memory cells of a number ofmemory cells. The memory block being divided into a number ofsub-blocks, each of the sub-blocks having non-overlapping ones of thememory cell strings. Each of the sub-blocks further includes arespective one of a number of segmented sources. The respective one ofthe number of segmented sources being coupled to the memory cell stringsof the respective sub-block. The segmented sources of the block areelectrically isolated from each other. Respective drain select devicesare coupled to the memory cell strings of the respective sub-block. Eachof the drain select devices has an asymmetric dopant profile.

In at least some of the embodiments of the apparatus, the asymmetricdopant profile is configured to prevent an erase disturb of non-selectedones of the sub-blocks during an erase operation.

As used herein, the term “or” may be construed in an inclusive orexclusive sense. Additionally, although various exemplary embodimentsdiscussed above focus on a 3D NAND memory device, the embodiments aremerely given for clarity in disclosure, and thus, are not limited toNAND memory devices or even to memory devices in general.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract allowing the reader to quickly ascertainthe nature of the technical disclosure. The abstract is submitted withthe understanding that it will not be used to interpret or limit theclaims. In addition, in the foregoing Detailed Description, it may beseen that various features are grouped together in a single embodimentfor the purpose of streamlining the disclosure. This method ofdisclosure is not to be interpreted as limiting the claims. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separate embodiment.

What is claimed is:
 1. An apparatus comprising: a block of memory havingsub-blocks that share a common data line, each of the sub-blocks of theblock of memory corresponding to a respective one of a number ofsegmented sources, each of the segmented sources of the block of memorybeing electrically isolated from the other segmented sources of theblock of memory, each of the sub-blocks of the block of memory having arespective number of strings of memory cells, the sub-blocks of theblock of memory each sharing a common source select line, the sub-blocksfurther having respective drain select devices coupled to the memorycell strings of the respective sub-block, the drain select deviceshaving an asymmetric dopant profile.
 2. The apparatus of claim 1,wherein the sub-blocks of the block of memory share a number of commonaccess lines, wherein each of the common access lines corresponds to arespective one of the strings of memory cells in the block of memory. 3.The apparatus of claim 1, wherein each of the strings of memory cells iscoupled to the common data line through the respective drain selectdevice and to the respective segmented source through a respectivesource select device, wherein the source select devices have a higherbreakdown voltage than the drain select devices.
 4. The apparatus ofclaim 1, wherein the drain select devices within each of the sub-blocksare electrically isolated from the drain select devices in othersub-blocks.
 5. The apparatus of claim 3, wherein the source selectdevices in each of the sub-blocks are electrically coupled to oneanother.
 6. The apparatus of claim 3, wherein the SGD junction on thedata line side has a junction breakdown voltage that is asymmetric withreference to the SGS junction on the source side.
 7. The apparatus ofclaim 1, wherein the apparatus is configured to: apply a first biasvoltage to the segmented source of a sub-block of the block of memoryselected to be erased during an erase operation; and apply a second biasvoltage to the segmented source of a sub-block of the block of memorynot selected to be erased during the erase operation, the first biasvoltage being greater than the second bias voltage.
 8. The apparatus ofclaim 1, wherein the sub-blocks of the block of memory do not share amemory cell.
 9. A three-dimensional device comprising multiple tiers ofmemory cells, the three-dimensional device comprising: a first sub-blockof a block of memory, the first sub-block including a first number ofmemory cell strings and a first segmented source; and a second sub-blockof the block of memory, the second sub-block including a second numberof memory cell strings and a second segmented source, the first andsecond segmented source being electrically isolated, the first sub-blockand the second sub-block of the block of memory each sharing a commonsource select line, the first number of memory cell strings and thesecond number of memory cell strings being coupled to a common data linethrough a number of drain select devices, each of the drain selectdevices having an asymmetric dopant profile.
 10. The three-dimensionaldevice of claim 9, wherein each of the first number of memory cellstrings is coupled to a respective one of a first number of drain selectdevices and wherein each of the second number of memory cell strings iscoupled to a respective one of a second number of drain select devices.11. The three-dimensional device of claim 10, wherein the source selectdevices have a higher breakdown voltage than the drain select devices.12. The three-dimensional device of claim 10, wherein each of the firstnumber of memory cell strings is coupled to a common data line through arespective one of the first number of drain select devices and whereineach of the second number of memory cell strings is coupled to thecommon data line through a respective one of the second number of drainselect devices.
 13. The three-dimensional device of claim 12, whereinthe device is configured to erase a selected one of the first sub-blockand the second sub-block separately from a non-selected one of the firstsub-block and the second sub-block by applying separate bias voltages tothe first and second segmented sources.
 14. The three-dimensional deviceof claim 13, wherein the device is configured to apply a bias voltage tothe segmented source of the selected one of the sub-blocks that ishigher than a bias voltage applied to the segmented source of thenon-selected one of the sub-blocks.
 15. The three-dimensional device ofclaim 14, wherein the device is further configured to erase a selectedone of the first sub-block and the second sub-block separately from anon-selected one of the first sub-block and the second sub-block byfloating drain select lines coupled to the drain select devices of theselected one of the sub-blocks and by applying a bias voltage to drainselect lines coupled to the drain select devices of the non-selected oneof the sub-blocks.
 16. The three-dimensional device of claim 15, whereinthe bias voltage that the device is configured to apply to the drainselect lines coupled to the drain select devices of the non-selected oneof the sub-blocks is no more than 75% of the bias voltage the device isconfigured to apply to the segmented source of the selected one of thesub-blocks.
 17. An apparatus, comprising: a block of memory including afirst sub-block and a second sub-block, the first sub-block and thesecond sub-block including a first number of memory cell strings and asecond number of memory cell strings, respectively, the first number ofmemory cell strings and the second number of memory cell strings beingcoupled to a common data line through a number of drain select devices,each of the drain select devices having an asymmetric dopant profile,the block of memory further comprising: a first segmented source coupledto the first number of memory cell strings in the first sub-blockthrough a first number of source select devices; and a second segmentedsource coupled to the second number of memory cell strings in the secondsub-block through a second number of source select devices, the sourceselect devices having a higher breakdown voltage than the drain selectdevices.
 18. The apparatus of claim 17, wherein the asymmetric dopantprofile in the drain select devices is configured to prevent a reversebias condition in a channel of the memory cell strings in one of thesub-blocks that is not selected for an erase operation.
 19. Theapparatus of claim 17, wherein the block further comprises common datalines, common access lines, and common source select lines that areshared between each of the sub-blocks.
 20. The apparatus of claim 17,wherein the block further comprises at least one of segmented datalines, segmented access lines, and segmented source select lines.
 21. Anapparatus comprising: a memory block including a number of memory cellstrings, each of the memory cell strings including respective memorycells of a number of memory cells, the memory block being divided into anumber of sub-blocks, each of the sub-blocks comprising non-overlappingones of the memory cell strings, each of the sub-blocks furthercomprising: a respective one of a number of segmented sources, therespective one of the number of segmented sources being coupled to thememory cell strings of the respective sub-block, the segmented sourcesof the block being electrically isolated from each other; and respectivedrain select devices coupled to the memory cell strings of therespective sub-block, each of the drain select devices having anasymmetric dopant profile.
 22. The apparatus of claim 21, wherein theasymmetric dopant profile is configured to prevent an erase disturb ofnon-selected ones of the sub-blocks during an erase operation.
 23. Theapparatus of claim 21, wherein the apparatus is configured to bias thedrain select devices of a selected one of the sub-blocks with adifferent signal than the drain select devices of a non-selected one ofthe sub-blocks.